I asked the question here somewhere too, and got no response 🙁
So I bought the normal one. The air gap between the can magnets and the arm is a couple of mm, so I’m guessing “thick” refers to thicker can magnets that give a stronger mag field and smaller air gap.
Thicker/stronger/closer mags should give an increase in torque and efficiency, but will most likely bring the max rpm down a bit.
I built up the fabled Plasmatomic motor ( http://woahnelly.com/plasmatomic/index.htm ) using the normal Atomic can, and it goes extrememly well 😀